Implantable piezoelectric hearing aid

ABSTRACT

AN IMPLANTABLE HEARING AID APPARATUS IS DESCRIBED USING A PIEZOELECTRIC TRANSDUCER DEVICE. ONE EMBODIMENT OF THE DEVICE IS A BENDABLE PIEZOELECTRIC MEMBER WHICH MAY BE INSERTED BETWEEN TWO BONES IN THE OSSICULAR CHAIN OF THE MIDDLE EAR FOR MOVEMENT OF SUCH BONES IN ACCORDANCE WITH AN AUDIO FREQUENCY ELECTRICAL SIGNL APPLIED TO SUCH TRANSDUCER. ANOTHER EMBODIMENT OF THE TRANSDUCER MEMBER US A CYLINDRICAL PIEZOELECTRIC MEMBER WHICH ELONGATES WHEN A SIGNAL IS APPLIED THERETO FOR MOVEMENT OF THE OSSICULAR BONES. THE TRANSDUCER MAY ALSO BE USED AS A PICKUP DEVICE TO SENSE THE MECHANICAL MOVEMENT OF THE OSSICULAR BONES AND PRODUCE A CORRESPONDING ELECTRICAL OUTPUT SIGNAL WHICH MAY BE APPLIED TO THE NERVES OF THE INNER EAR.

Jan. 23, 1973 J. M. EPLEY 3,712,962

IMPLANTABLE PIEZOELECTRIC HEARING AID Filed April 5, 1971 3 Sheets-Sheet1 FIG I SKI N IMPLANTED EXTERNAL RECE'VER Jfif 'F MICROPHONE JOHN M.EPLEY INVENTOR BUCKHORN, BLORE, KLARQUIST & SPARKMAN ATTORNEYS Jan. 23,1973 J. M. EPLEY IMPLANTABLE PIEZOELECTRIC HEARING AID 3 Sheets-Sheet 2Filed April 5, 1971 OUTPUT JOHN M. EPLEY.

INVENTOR BY BUCKHORN, BLORE, KLARQUIST & SPARKMAN ATTORNEYS Jan. 23,1973 J. M. EPLEY IMPLANTABLE PIEZOELECTRIC HEARING AID 3 Sheets-Sheet 3Filed April 5, 1971 JOHN M. EPLEY INVENTOR BlKKHORN, BIO/(l, KIARQUISI &SIARKMAN ATTORNEYS United States Patent Ofice US. Cl. 179-107 R 17Claims ABSTRACT OF THE DISCLOSURE An implantable hearing aid apparatusis described using a piezoelectric transducer device. One embodiment ofthe device is a bendable piezoelectric member which may be insertedbetween two bones in the ossicular chain of the middle ear for movementof such bones in accordance with an audio frequency electrical signalapplied to such transducer. Another embodiment of the transducer memberis a cylindrical piezoelectric member which elongates when a signal isapplied thereto for movement of the ossicular bones. The transducer mayalso be used as a pickup device to sense the mechanical movement of theossicular bones and produce a corresponding electrical output signalwhich may be applied to the nerves of the inner ear.

BACKGROUND OF THE INVENTION The subject matter of the present inventionrelates generally to implantable hearing aid apparatus using apiezoelectric transducer, and in particular to such an apparatus inwhich the piezoelectric transducer is used to move the bones of theossicular chain in the middle ear when an electrical input signal isapplied thereto, or to produce an electrical output signal in responseto movement of such bones so that such output signal may be applied tothe nerves of the inner ear.

The implantable hearing aid apparatus of the present invention is animprovement over conventional hearing aid apparatus in that it iscompletely hidden from view so that it does not have the unsightlyappearance of conventional hearing aids. In addition, the presenthearing aid employs a piezoelectric transducer which is very compact sothat it can be positioned between two bones of the ossicular chainwithout any appreciable impairment of movement of such bones during thenormal operation of the ear in response to sounds. Previous implantablehearing aids have employed piezoelectric transducers but they were notof the bending type and were not positioned between the bones of theossicular chain. Thus, as shown on page 54 of the article by Jako andJensen, in the publication American Academy of Opthalmology andOtolaryngology, Course 319, Conservative Tympanoplasty, published Oct.1, 1966, one prior art device included a piezoelectric transducer usedas a microphone pickup in the tympanic membrane of the middle ear toproduce an output signal which is applied to a piezoelectric outputtransducer mounted in the oval window of the inner ear to move the fluidin the cochlea of the inner ear. The piezoelectric transducer device ofthe present invention is much more efficient and requires less powerthan the prior art apparatus. Another advantage is that there is lessharmonic distortion in the hearing aid apparatus of the presentinvention.

It is therefore one object of the present invention to provide improvedimplantable hearing aid apparatus which may be completely hidden fromview including a compact piezoelectric transducer device.

Another object of the present invention is to provide such a hearing aidapparatus in which the piezoelectric transducer is a bendable devicewith high efliciency and low power dissipation.

3,712,962 Patented Jan. 23, 1973 A further object of the invention is toprovide such a hearing aid apparatus in which the piezoelectrictransducer device is adapted to be inserted between two bones of theossicular chain so that it does not interfere with the movement of theossicular chain in response to sound vibrations during normal operationof the ear.

Still another object of the invention is to provide such a hearing aidapparatus of low harmonic signal distortion and of a relatively simpleand inexpensive construction.

BRIEF DESCRIPTION OF DRAWINGS Other objects and advantages of thepresent invention will be apparent from the following detaileddescription of certain preferred embodiments thereof and from theattached drawings, of which:

FIG. 1 is a schematic diagram showing one embodiment of the implantablehearing aid apparatus of the pres ent invention including a bending typeof piezoelectric transducer;

FIG. 2 is a perspective elevation view of the transducer device used inthe hearing aid apparatus of FIG. 1;

FIG. 3 is a section view taken along the line 33 of FIG. 2;

FIG. 4 is an enlarged section view taken along the line 44 of FIG. 3;

FIG. 5 is a schematic diagram of another embodiment of the hearing aidapparatus of the present invention in which the piezoelectric transduceris used as a pickup device to produce an output signal in response tomovement of the bones of the ossicular chain;

FIG. 6 is an elevation view of another embodiment of the piezoelectrictransducer device used in the apparatus of FIGS. 1 and 5;

FIG. 7 is a horizontal section view taken along line 7-7 of FIG. 6;

FIG. 8 is an enlarged vertical section view line 8-8 of FIG. 7;

FIG. 9 is a perspective view of a further embodiment of a piezoelectrictransducer which may be employed in the hearing apparatus of the presentinvention;

FIG. 10 is an enlarged section view taken along line 10-10 of FIG. 9;

FIG. 11 is a perspective view of still another embodiment of apiezoelectric transducer employed in the hearing aid apparatus of thepresent invention; and

FIG. 12 is an enlarged horizontal section view taken along line 1212 ofFIG. 11.

DESCRIPTION OF PREFERRED EMBODIMENTS As shown in FIGS. 1 to 4, oneembodiment of the implantable hearing aid apparatus of the presentinvention includes a piezoelectric transducer device 10 of the bendabletype shown in US. Pat. 2,841,722 of Gravely granted July 1, 1958, whichis connected through leads 11 and 13 to the audio frequency signaloutput of an implanted radio receiver circuit 12. The receiver circuitis coupled by an internal antenna 14 beneath an outer layer 16 of theskin on the head of the user to an external antenna 18 of a radiotransmitter 20 positioned outside the body of such user. This externaltransmitter and associated amplifier is connected at its input to amicrophone 22 and may be provided as a compact unit also containing thepower supply batteries for such transmitter which may be completelyhidden from view in the clothes or the eyeglasses of the user. Thus, theimplantable hearing aid apparatus of the present invention avoids theunsightly appearance of conventional hearing aids.

The receiver 12 may be self-biased by charging power supply capacitorstherein with the radio frequency signal transmitted from the transmitter20' using a circuit similar taken along to that shown in US. Pat.3,209,081 of Ducote et al., granted Sept. 28, 1965, which also shows asuitable transmitter. The receiver circuit may be made extremely smalland with low power dissipation by using a semiconductor integratedcircuit including field eflfect transistors. The implanted receiver 12is encapsulated in a covering of suitable inert plastic material, suchas epoxy resin or silicone rubber. Of course, the covering material mustbe waterproof and implantable into the tissue without causing infectionor damage. It should be noted that it may be preferable to providerechargeable batteries within the implanted receiver 12 in which case acharging coil and associated rectifiers are provided with such chargingcoil positioned adjacent the outer surface of the skin 12 so that suchbattery may be recharged through an inductance coil positioned adjacentto such charging coil from an external A.C. power supply.

As shown in FIG. 1, the transducer is mounted with its free ends 24positioned between two bones of the ossicular chain in the middle ear,such as the stapes 26 and the incus 28. The transducer device 10 is notfixed to any bone or other element of the ear, and as a result, does notinterfere with the normal operation of the ossicular chain intransmitting sound vibrations from the tympanic membrane 30 through themalleus 32, incus 28 and stapes 26 to the inner ear. This has theadvantage that the user, who hears normally at some frequencies, or onlyhas a partial deafness may still hear in a normal manner after thehearing aid is implanted.

As shown in FIGS. 2, 3 and 4, the piezoelectric transducer device 18includes two pending piezoelectric members 34 and 36 sold under thetrademark Bimorph by the Clevite Corporation, Piezoelectric Division, ofBedford, Ohio. Each of the piezoelectric members 34 and 3'6 is formed bya pair of piezoelectric ceramic plates 38 and 40 which are separated byan intermediate conducting layer 42 and are provided with outerconducting layers 44 and 46. As shown in FIG. 4, the piezoelectricceramic plates 38 and 40 may be connected in parallel with the two outerconducting layers 44 and 46 being connected together at one terminallead 48 of the receiver 12, while the intermediate conducting layer 42is connected to the other lead 50 of the receiver. As a result of polingthe piezoelectric ceramic material in the same direction, both of theceramic plates 38 and 40 in each of the members 34 and 36 bend in thesame direction when a signal voltage is applied to terminal leads 48 and50. However, the two piezoelectric members 34 and 36 are oriented tobend in opposite directions for greater efiiciency. The crystallinepiezoelectric ceramic plates 38 and 40 are poled in the same directionin a conventional manner by applying a DC. electrical field of theproper polarity during their formation. Of course, other piezoelectricmaterials can be employed, such as quartz and Rochelle salt, which donot require this poling.

'It should be noted that while FIG. 4 shows a parallel connection of thetwo piezoelectric ceramic plates 38 and 40, it is also possible toconnect them in series in which case the lower conductive layer 46 isconnected to terminal 50 and the upper layer 44 remains connected toterminal 48 while intermediate layer 42 is disconnected. In this seriesconnection, the piezoelectric ceramic material 38 and 40 is poled inopposite directions in order to produce the required bending.

As shown in FIG. 3, the free ends 24 of each of the piezoelectricmembers 34 and 36 are provided with a relatively thick metal plate 52attached to the inner conductive coating 46 by epoxy resin or othersuitable means. A housing or guide member 54 of suitable plasticmaterial, such as Teflon, is attached to the outer surface of thatportion of each metal plate 52 extending beyond the ends of thepiezoelectric members 34 and 36. The guide member 54 is provided with acentral aperture 56 for receiving the adjacent ends of the bones 26 and28 of the ossicular chain between which the transducer is inserted. Theguide members 54 are made of soft plastic so that they may be trimmed tothe proper size during the implant operation.

A resilient spacer member 58 in the form of a cylindrical wedge oftriangular cross section is provided between the two metal plates 52 tohold such plates in engagement with bones 26 and 28. The spacer member58 may be made of a silicone rubber material or other resilient materialso that the spacer acts as a damper and connterpoise spring. A fixedrigid spacer 60 of metal is attached between the other end of thepiezoelectric members 34 and 36 by epoxy resin. The terminal lead wires48 and 50 are attached to the same end of such piezoelectric members bya small quantity or bead 62 of epoxy resin which acts as insulatingmaterial. The wires 48 and 50 are connected to the conductive layers 42,44 and 46 by soldering or a conductive epoxy resin underlayer containinga filling of silver particles or other suitable conductive material.

As shown in FIG. 5 in another embodiment of the invention, thepiezoelectric transducer device 10' is employed as a pickup devicehaving a pair of output conductors '64 and 66 which transmit theelectrical output signal produced by such transducer when the ossicules26, 28 move the piezoelectric members 34' and 36'. The audio-frequencyoutput signal produced by the transducer 10' is transmitted through anamplifier 68 to a pair of output terminals 70 and 72 which may beconnected directly to nerves in the inner ear or to a piezoelectricpiston device mounted on the oval window of the inner ear for moving thefluid within the inner ear. Any suitable, implantable amplifier circuitmay be employed for amplifier 68 so long as it is capable of low powerdissipation to enable long battery life.

As shown in FIGS. 6, 7 and 8, the piezoelectric transducer device 10' ofFIG. 5 may be similar to that of FIGS. 2, 3 and 4 except that eachpiezoelectric member 34 and 36' is formed with a single piezoelectricceramic plate 74 which is provided with a conductive coating 76 ofsilver or the like on one side and is bonded to a metal plate 78 ofstainless steel on its other side by epoxy resin or other suitablematerial. This bendable, piezoelectric member 74 is also sold by CleviteCorporation under their trademark Unimorph. Bending of the piezoelectricmembers 34 and 36' occurs because the metal plate 78 is of fixed lengthand is attached along the entire length of the piezoelectric ceramicmember 74. It should be noted that the metal plate 78 extends beyond theend of the ceramic member 74 and also serves as the metal plates onwhich the guide members 54 of plastic material are attached. Of course,the modified piezoelectric transducer device 10 of FIGS. 6-8 can also beemployed in the hearing aid apparatus of FIG. 1 and, similarly, thepiezoelectric transducer device 10 of FIGS. 2 through 4 can be employedin the hearing aid apparatus of FIG. 5.

-A third embodiment of the piezoelectric transducer device 10" is shownin FIG. 9 and consists of a single piezoelectric member which may havetwo piezoelectric ceramic layers 38 and 40 like member 34 of FIGS. 3 and4. Alternatively, transducer device 10" may be like piezoelectric member34 of FIGS. 7 and 8. In this embodiment, the transducer device 10" has afixed end at epoxy resin bond 62 which is attached to a bone 80 or otherfixed anchor point within the ear. The free end of such transducer isprovided with a metal plate 82 having a threaded hole through which ametal screw guide member 84 extends. The guide member 84 is hollow toprovide a housing, such as a conical cavity, into which the stapes bone26 fits. The guide member 84 is adjusted by a threaded shank portion 86extending through such threaded hole to enable adjustment of the guidemember relative to the stapes bone 26. Thus, vibration of thepiezoelectric transducer device 10" due to the application of an inputsignal through Wires 48 and 50 causes a corresponding vibration of thestapes bone 26 even when the incus bone has been removed by surgery.

As shown in FIGS. 11 and 12, still another embodiment of thepiezoelectric transducer device 10" may be in the form of a hollow,cylindrical tube 8 8 of piezoelectric ceramic material having a pair ofelectrodes 90 and 92 coated on its inner and outer surfaces which areconnected, respectively, to the lead wires 48 and 50. In this embodimentof the invention, the piezoelectric transducer device 10" is positionedbetween the incus bone 28 and the footplate portion 94 of the stapesbone 26 when the arch portion of such stapes bone has been removed bysurgery, such are portion being shown in phantom lines in FIG. 11. Thetubular ceramic member 88 expands and contracts longitudinally inresponse to an electrical signal applied thereto by lead wires 48 and 50and thereby oscillates the bones of the ossicular chain in the samemanner as the embodiment of FIGS. 1 to 4. It will be obvious to thosehaving ordinary skill in the art that many changes may be made in thedetails of the preferred embodiments of the present invention withoutdeparting from the spirit of the invention. Therefore, the scope of thepresent invention should only be determined by the following claims.

I claim: 1. An implantable hearing aid apparatus in which theimprovement comprises:

transducer means including a piezoelectric transducer device adapted tobe implanted in an ear; and

mounting means for mounting the transducer device between two movablebones in the ossicular chain of the ear to cause movement of said bonesand said device together when an electrical signal is applied to saiddevice, said piezoelectric device being free of any fixed connectionwhich would prevent normal movement of said bones in response to sound.

2. Apparatus in accordance with claim 1 including input signal means forapplying an audio frequency electrical signal to the transducer deviceto cause said device to move said bones in response to the audio signal.

3. Apparatus in accordance with claim 1 including output signal meansfor transmitting an audio frequency electrical signal from thetransducer device when said device is moved by said bones.

4. Apparatus in accordance with claim 1 in which the transducer deviceis a piezoelectric cylinder member which is provided with axial movementwhen the audio signal is applied thereto.

5. Apparatus in accordance with claim 1 in which the transducer deviceincludes at least one bendable piezoelectric bar member.

6. Apparatus in accordance with claim in which the transducer deviceincludes a pair of bar members of piezoelectric material which bend inopposite directions when said audio signal is applied thereto, said barmembers having interconnected ends attached together and free ends whichare free to move relative to each other.

.7. .An implantable hearing aid apparatus in which the improvementcomprises:

a piezoelectric transducer device adapted to be implanted in an earincluding a pair of bar members; and

mounting means including a pair of. connectors on the free ends of saidbar members which are adapted to be inserted between the two bones inthe ossicular chain to provide the sole support for the transducerdevice.

8. Apparatus in accordance with claim 7 in which the connectors aremetal plates attached to the bar members with end portions extendingfrom the free ends of said bar members.

9. Apparatus in accordance with claim 8 in which the end portions of themetal plates are each attached at its outer surface to a housing memberprovided with a central opening for receiving one of said bones.

10. Apparatus in accordance with claim 9 in which the housing member isof plastic material.

11. Apparatus in accordance with claim 8 in which each of the metalplates is fixedly attached along the entire length of one side of thebar member, a conductive coating is provided on the opposite side ofsaid bar member, and said bar member is made of a single layer ofpiezoelectric ceramic material.

12. Apparatus in accordance with claim -8 in which each of the metalplates is fixedly attached along only a short portion of one side of thebar member, a pair of conductive coatings are provided on the oppositesides of said each bar member, and said bar member includes a pluralityof layers of piezoelectric ceramic material separated by an intermediateconductive layer.

13. Apparatus in accordance with claim 7 in which the pair of barmembers have their interconnected ends separated by a rigid spacermember and have their free ends separated by a resilient spacer member.

14. Apparatus in accordance with claim 13 in which the resilient spacermember is made of silicone plastic material.

15. Apparatus in accordance with claim 2 in which the input signal meansincludes an implantable receiver circuit which produces said audiosignal at its output.

16. Apparatus in accordance with claim 15 which also includes a remotenon-implantable transmitter circuit for transmitting signals to saidreceiver circuit.

17. Apparatus in accordance with claim 3 in which the output signalmeans includes an implantable amplifier circuit.

References Cited UNITED STATES PATENTS 3,594,514 7/197'1 Wingrove l79107R 2,928,069 3/1960 Petermann 310--8.3 X 3,181,016 4/1965 Rosenman 3l08.33,093,710 6/1963 Ten Eyck 179-110 A THOMAS W. BROWN, Primary ExaminerUS. Cl. X.R. 310-83

